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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
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NASA NTRS1984

Control of forward swept wing configurations dominated by flight-dynamic/aeroelastic interactions

An active control system concept for an aeroelastic wind-tunnel model of a statically unstable FSW configuration with wing-mounted stores is developed to provide acceptable longitudinal flying qualities while maintaining adequate flutter speed margin. On FSW configurations, the inherent aeroelastic wing divergence tendency causes strong flight-dynamic/aeroelastic interactions that in certain cases can produce a dynamic instability known as body-freedom flutter (BFF). The carriage of wing-mounted stores is shown to severely aggravate this problem. The control system developed combines a canard-based SAS with an Active Divergence/Flutter Suppression (ADFS) system which relies on wing-mounted sensors and a trailing-edge device (flaperon). Synergism between these two systems is exploited to obtain the flying qualities and flutter speed objectives.

Rimer, M.↗
NASA NTRS1984

Non-local Origin of a Substantial Portion of the Soft X-ray Background

Comparison of the SAS-3 soft X-ray sky survey with the 21-cm neutral hydrogen survey confirms the well-known anticorrelation between the counting rates in the C-band (0.10-0.28 keV) and the column density of neutral hydrogen, and demonstrates that this anticorrelation is significant on all angular scales ranging from that of the general trend from the galactic equator to the poles down to the angular resolution of the detector (2.07 FWHM). Numerous instances of what appear to be soft X-ray shadows of nearly (100-300 pc) 21-cm features, and several bright X-ray regions coincident with holes in the interstellar medium are included in this general correlation. The final set of selected data has an exposure of 2.2 x 10 to the 4th power/sq cm s sr, a sky coverage of 80%, and is free of spurious effects due to charged particles and solar radiations. The validity of the two-component model of the X-ray background, introduced by Davidsen et al. (1977) is examined. In this model the C-band intensity in a given direction is represented as a sum of a constant term, I sub 1, due to unattenuated emission from a local hot bubble in which the solar system is immersed, and a term, I sub 2 exp (N sub H sub th) , due to emission from a diffuse source beyond the neutral hydrogen 2.g., the galactic corona).

Clark, G. W.↗
NASA NTRS1984

The galactic gamma-ray distribution: Implications for galactic structure and the radial cosmic ray gradient

The radial distribution of gamma ray emissivity in the Galaxy was derived from flux longitude profiles, using both the final SAS-2 results and the recently corrected COS-B results and analyzing the northern and southern galactic regions separately. The recent CO surveys of the Southern Hemisphere, were used in conjunction with the Northern Hemisphere data, to derive the radial distribution of cosmic rays on both sides of the galactic plane. In addition to the 5 kpc ring, there is evidence from the radial asymmetry for spiral features which are consistent with those derived from the distribution of bright HII regions. Positive evidence was also found for a strong increase in the cosmic ray flux in the inner Galaxy, particularly in the 5 kpc region in both halves of the plane.

Harding, A. K.↗
NASA NTRS1985

Oceanographic and meteorological research based on the data products of SEASAT

Reservations were expressed concerning the sum of squares wind recovery algorithm and the power law model function. The SAS sum of squares (SOS) method for recovering winds from backscatter data leads to inconsistent results when V pol and H pol winds are compared. A model function that does not use a power law and that accounts for sea surface temperature is needed and is under study both theoretically and by means of the SASS mode 4 data. Aspects of the determination of winds by means of scatterometry and of the utilization of vector wind data for meteorological forecasts are elaborated. The operational aspect of an intermittent assimilation scheme currently utilized for the specification of the initial value field is considered with focus on quantifying the absolute 12-hour linear displacement error of the movement of low centers.

Pierson, W. J., Jr.↗
NASA NTRS1985

Search for periodicities near 59 s in the COS-B gamma-ray data of 2CG195+04 (Geminga)

The COS-B data relating to five observations in the general direction of Geminga, spanning 6.7 years, were searched for pulsation near 59 s. The SAS-2 indication is not confirmed. An indication of a 59 s pulsation in the gamma ray emission from 2CG195+04 (Geminga) was reported. Early analysis of COS-B data supported the result while later improved statistics did not confirm it. Subsequently, detection of a 59 s pulsation in the emission from the direction of Geminga at ultra high gamma and X-rays was reported. Geminga was identified with the X-ray source 1E0630+128. The final COS-B data on Geminga which was observed five times for a total of 214 days are reported.

Buccheri, R.↗
NASA NTRS1985

Cosmic gamma rays from quasars

The diffuse gamma radiation consists of the galactic and extragalactic components. The latter component is of special interest on account of its cosmological significance. Following the method recently proposed to estimate the gamma ray flux from galaxy clusters, and the detection of gamma rays from the quasars 3C273, the data base of the SAS II satellite was used to estimate the contribution from quasars to the extragalactic gamma ray flux. It is shown that quasars as a whole are significant gamma ray contributors, the average gamma ray flux per quasar in the energy range 35 MeV to 100 Mev being (1.3 + or - 0.9) x .00001 cm(-2)s(-1)sr(-1).

Lau, M. M.↗
NASA NTRS1985

The galactic gamma-ray distribution and the radial cosmic ray gradient

The radial distribution is derived of gamma ray emissivity and the cosmic ray intensity in the Galaxy using the final SAS-2 results, the recently corrected COS-B results, and recent CO surveys of the Northern and Southern Galactic Hemispheres. In addition to the 5 kpc ring of enhanced emission, there is evidence for spiral features. A strong increase in the cosmic ray flux is found in the inner Galaxy, particularly in the 5 kpc region, in both halves of the plane.

Harding, A. K.↗
NASA NTRS1985

Giant molecular clouds as regions of particle acceleration

One of the most interesting results of investigations carried out on the satellites SAS-II and COS-B is the discovery of unidentified discrete gamma sources. Possibly a considerable part of them may well be giant molecular clouds. Gamma emission from clouds is caused by the processes with participation of cosmic rays. The estimation of the cosmic ray density in clouds has shown that for the energy E approx. = I GeV their density can 10 to 1000 times exceed the one in intercloud space. We have made an attempt to determine the mechanism which could lead to the increase in the cosmic ray density in clouds.

Dogiel, V. A.↗
NASA NTRS1984

HEAO 1 high-energy X-ray observations of three bright transient X-ray sources H1705-250 (Nova Ophiuchi), H1743-322, and H1833-077 (Scutum X-1)

The bright X-ray transients H1705-250 (Nova Ophiuchi) and H1743-322 in the energy range 12-180 keV were observed, and the presence of high-energy spectral components was revealed. On the basis of X-ray spectra in the 1-10 keV range, transients are classified as 'soft' (kT = 4 keV) or 'hard' (kT = 17 keV); and both H1705-250 and H1743-322 should be in the 'soft' category. Data have been reexamined for the archetypal 'soft' transient A0600-00 taken by the SAS 3 satellite, but no evidence is found there for a high-energy spectral component. Thus consideration of a wider X-ray energy range makes the 'hard'/'soft' distinction between X-ray transients much less clear.

Cooke, B. A.↗
NASA NTRS1983

Diffuse galactic emission of high energy gamma rays

A study of the gamma-radiation produced by the interaction of cosmic rays with the interstellar matter and photons is extended, based on recent COS-B satellite results and background estimates (1982) and evaluations of the 21-cm radiation in the Galaxy. Gamma-ray intensities predicted over the latitude range of -10 to 10 degrees for energy ranges 70-150, 150-300, and 300-5000 MeV agree well with the COS-B longitude distributions. The agreement suggests that the radial distribution of the emission, calculated from the model, is also approximately correct. The energy spectrum is calculated using COS-B and SAS-2 data. Finally, it is noted that contribution by the arms on the far side of the Galaxy for small galactic latitudes (between -0.4 and +0.4 degrees) makes it possible to identify very large far-side molecular clouds.

Kniffen, D. A.↗
NASA NTRS1983

Origin of diffuse gamma-ray background

It is shown that the observed spectrum of the diffuse gamma-ray background could be accounted for by unresolved active galaxies even with no evolution, if their spectra are described by a spherical accretion/shock acceleration model (1983) and are steepened by photon-photon pair production interactions at high energies. The model is based on HEAO-1 and SAS-2 observations in the region of 2 to 165 keV and above 30 MeV. The model predicts a higher flux of high-energy neutrinos from active galaxies than models in which electrons are accelerated directly. It is noted that several active galaxies should be detectable by the Gamma-Ray Observatory, making it possible to determine the actual contribution of active galaxies to the diffuse gamma-ray background.

Protheroe, R. J.↗
NASA NTRS1983

Detection of cosmic ray electrons above 10 to 14th eV using gamma ray observatories

A quantitative evaluation of high energy gamma ray observatories for the study of cosmic ray electrons is made. This is based on the principle that the synchrotron photons emitted by the electrons in the earth's magnetic field is collinear in the detector. It is shown that the size and the gamma ray detection efficiency of the SAS II instrument is so small, that no useful information can be derived from it. On the other hand, one may be able to set useful upper limits to the flux of electrons by making use of the high energy gamma ray detector in the GRO.

Stephens, S. A.↗
NASA NTRS1984

The 41.5 day binary X-ray pulsar 4U 1223 - 62 (GX 301 - 2)

Ariel 5 and SAS 3 X-ray pulse timing data for the 700 s X-ray pulsar 4U 1223 - 62 (GX 301 - 2) are reexamined in order to deduce the orbital elements of this system. The Ariel 5/SAS 3 arrival times are first reanalyzed to obtain the best solution for an orbital period close to 41.5 days and to estimate the uncertainties in it caused by unknown variations in the underlying pulse period. Spectral measurements by OSO 8 and HEAO 1 at a variety of orbital phases are presented and the origin of an unabsorbed, unpulsed soft component is discussed. OSO 8 observations of occasions when the amplitude and shape of the pulse profile changed dramatically are discussed. The global X-ray properties of the system are explained in terms of a simple stellar wind accretion model, and the interaction of the inflowing material with the neutron star magnetosphere is considered.

White, N. E.↗
NASA NTRS1985

On fast X-ray rotators with long-term periodicities

The support of previous SAS 3 spacecraft observations by new data gathered by the Monitor Proportional Counter aboard the HEAO 2 spacecraft indicates that the pulse period history of the 13.5 sec-pulsing X-ray source LMC X-4 is consistent with standard accretion and torque models only if LMC X-4 is a fast rotator for which the accretion torques nearly cancel. This result leads to a neutron star magnetic field strength estimate of about 1.2 x 10 to the 13th G. Strong evidence is noted for Her X-1's status as a fast rotator, while SMC X-1 is probably an intermediate-to-fast rotator. In the context of slaved disk models for these objects, it is noted that the precession periods expected for the companion stars are significantly longer than the observed 1-2 month time scales; slaved disk models are thereby undermined.

Naranan, S.↗
NASA NTRS1985

The galactic gamma-ray distribution - Implications for galactic structure and the radial cosmic-ray gradient

The radial distribution of gamma ray emissivity in the Galaxy was derived from flux longitude profiles, using both the final SAS-2 results and the recently corrected COS-B results and analyzing the northern and southern galactic regions separately. The recent CO surveys of the Southern Hemisphere were used in conjunction with the Northern Hemisphere data, to derive the radial distribution of cosmic rays on both sides of the galactic plane. In addition to the 5 kpc ring, there is evidence from the radial asymmetry for spiral features which are consistent with those derived from the distribution of bright H II regions. Positive evidence was also found for a strong increase in the cosmic ray flux in the inner Galaxy, particularly in the 5 kpc region in both halves of the plane.

Harding, A. K.↗
NASA NTRS1986

An IBM PC-based math model for space station solar array simulation

This report discusses and documents the design, development, and verification of a microcomputer-based solar cell math model for simulating the Space Station's solar array Initial Operational Capability (IOC) reference configuration. The array model is developed utilizing a linear solar cell dc math model requiring only five input parameters: short circuit current, open circuit voltage, maximum power voltage, maximum power current, and orbit inclination. The accuracy of this model is investigated using actual solar array on orbit electrical data derived from the Solar Array Flight Experiment/Dynamic Augmentation Experiment (SAFE/DAE), conducted during the STS-41D mission. This simulator provides real-time simulated performance data during the steady state portion of the Space Station orbit (i.e., array fully exposed to sunlight). Eclipse to sunlight transients and shadowing effects are not included in the analysis, but are discussed briefly. Integrating the Solar Array Simulator (SAS) into the Power Management and Distribution (PMAD) subsystem is also discussed.

Emanuel, E. M.↗
NASA NTRS1985

New atmospheric temperature results from the Pioneer Venus entry probes

A new independent determination of Venus atmospheric temperatures, derived from auxiliary engineering measurements of the Small Probe Net Flux Radiometer (SNFR) instruments on board the three small Pioneer Venus entry probes, is presented. The temperature-measurement system and the thermal model needed to convert the raw measurements to atmospheric temperatures are described. The vertical temperature structure and horizontal temperature contrast results are compared graphically measured by the SAS instrument (Seiff et al., 1980), showing a high degree of agreement.

Sromovsky, L. A.↗
NASA NTRS1986

Orbital elements of the binary X-ray pulsar GX 301-2

X-ray outbursts from GX 301-2 were observed with Hakucho on two occasions during April and May 1982 and with Tenma in April 1984. Pulse arrival times measured with Hakucho were combined with those previously measured with Ariel 5 and SAS 3. The joint timing analysis of these data sets yields an orbital period of 41.5 days as the only acceptable solution; this is consistent with the period derived from the X-ray flaring events of the source. The orbital elements of the binary system, established from the joint timing analysis, are presented. The orbital solution suggests that all the peaks of X-ray flares observed during the past 10 yr occur at the orbital period, but consistently appear about 1.4 days before the time of periastron passage of the X-ray star.

Sato, N.↗